1. Field of the Invention
The present invention relates to a method for preparing a titanium-silicalite molecular sieve, and more particular to, a method for preparing a large-sized titanium-silicalite molecular sieve with high reactivity and a method for preparing a cyclohexanone oxime using the large-sized titanium-silicalite molecular sieve.
2. Description of the Prior Art
Crystalline titanium-silicalite molecular sieves are formed by incorporating titanium into the zeolite structure of silicon dioxide, and have the MFI structures, which are also named as the TS-1 molecular sieves. U.S. Pat. No. 4,410,501 discloses the preparation of this molecular sieve. Such molecular sieve is used as a catalyst in an oxidation reaction, wherein hydrogen peroxide is used as an oxidant. However, the hydrolysis rate of the titanium source is too fast to match the hydrolysis rate of the silicon source, such that the two materials may not mixed evenly, and the order degree of the material is decreased. Moreover, the titanium source may become anatase, and the catalyst is thus degraded. Therefore, it is important to have even mixing of materials and proper hydrolysis rates of the titanium source and the silicon source, and to avoid the formation of anatase.
Chemical Engineering Journal 156 (2010) 562-570, Journal of Materials Science 37 (2002) 1959-1965, J. Phys. Chem. A 2009, 113, 15006-15015, Ind. Eng. Chem. Res. 48, 4334-4339, 2009 disclose UV-visible diffuse reflectance spectra of TS-1, wherein the peak at 220 nm represents the bonding of titanium-oxygen-silicon, and the peak at 330 nm represents the bonding of titanium-oxygen-titanium. The higher titanium content results in more significant peak at 330 nm. The MFI structure is based on the bonding of titanium-oxygen-silicon, and thus the conventional technology focused on the reduction of the bonding of titanium-oxygen-titanium, and developed the methods for lowering the titanium content. However, the lower titanium content results in fewer activity spots on the TS-1 molecular sieve and lower catalyst activity. The particle size of the conventional molecular sieve is about 0.2 μm. However, such catalyst applied in the industry (such as the preparation of cyclohexanone oxime from cyclohexanone, ammonia and hydrogen peroxide) needs to be improved.
Thus, the technologies have been developed to enlarge the particle size of the molecular sieve. U.S. Pat. Nos. 5,500,199, 6,106,803 and 6,524,984 disclose that small particles are aggregated by an inorganic adhesive agent, and then spray-dried. The particle size of the catalyst in these methods is enlarged; however, the active site of the catalyst is covered by the adhesive agent, the reactivity of the catalyst is decreased, and the amount of the catalyst in the reaction needs to be increased.
Hence, it is an urgent issue to develop a method for preparing a titanium-silicalite molecular sieve with a large particle size and high activity so as to facilitate the recovery of the molecular sieve, improve the usage efficiency of hydrogen peroxide, and favor the application in the industry.